Abstract: A defrosting control for a heat pump system utilizes a first temperature sensor mounted to the outdoor coil fan motor windings, a second sensor mounted to sense the outdoor ambient air temperature and a third sensor to sense the refrigerant temperature in the outdoor coil. The control circuitry determines the temperature difference of the first two sensors, representing the fan motor temperature rise, which increases dramatically when the outdoor coil is frosted; if the difference exceeds a selected abnormal temperature rise and the temperature sensed by the third sensor indicates frosting is likely to have occurred, the defrost cycle is initiated. The cycle is terminated when the temperature sensed by the third sensor indicates that all frost is likely to have melted.

Abstract: A suction-liquid heat exchanger for a heat pump is provided by utilizing an inner vessel as a suction line accumulator together with a surrounding high pressure outer vessel which is utilized as a receiver in the liquid line. Heat from the liquid refrigerant in the outer vessel is transferred to the cooler liquid accumulated in the inner vessel to vaporize it, preventing slugs of liquid refrigerant from entering the compressor. The exit and entry ports of the outer vessel are at different levels. This causes a greater amount of liquid refrigerant to remain in the outer vessel on heating mode operation than on reverse flow for cooling, thereby increasing the heat transfer to the accumulator as required for the greater volume of liquid in the suction line gas and compensating for the decreased quantity of refrigerant needed for heating.